A study of the precipitation distribution in coastal British Columbia is described and a technique is proposed for the reliable estimation of the frequency of rainfall generated floods from ungauged watersheds in the region. A multi-disciplinary investigation was undertaken encompassing the areas of hydrometeorology, meteorological modelling and hydrological modelling. Study components included analysis of long- and short-term precipitation in two medium sized watersheds located in southwestern coastal British Columbia; development of a 24-hour design storm for coastal British Columbia; generalization of the results over the coastal region of British Columbia; examination of the precipitation distribution during flood producing storms; identification of the applicability of a meteorological model for the estimation of short-term precipitation; and development of a physically-based stochasticdeterministic procedure for the estimation of flood runoff from ungauged watersheds of the region.
Based on an assessment of the atmospheric processes which affect climate, it was
found that the strong frontal storms which form over the North Pacific Ocean and travel
eastward generate the majority of the precipitation during the winter and fall months, whereas
convective rainshowers and weak frontal storms produce the dry summer period precipitation.
Examination of the annual, seasonal, and monthly precipitation in the two study
watersheds, the Seymour River and the Capilano River watersheds, showed that the variation
of annual and winter and fall precipitation with elevation follows a curvilinear pattern,
increasing up to middle position of the watersheds at an elevation of about 400 m and then
decreasing or leveffing off at the upper elevations. The summer precipitation is more
uniformly distributed over the watersheds than the winter precipitation and accounts for about 25% of the total annual precipitation. The Bergeron two-cloud mechanism has been identified as the dominant rainfall producing mechanism during the winter and fall months.
Analysis of regional data and results of other regional studies indicate that the
curvilinear pattern found in this study is more general and is similar for the whole of coastal
British Columbia and the coastal Pacific Northwest.
Study of the 175 storms in the Seymour River watershed showed that the individual
storm precipitation is distributed in a pattern similar to that of the annual precipitation and this
distribution pattern is not affected by the type of the event. Furthennore, the analysis showed
that the storm time distribution is not affected by the elevation, type of the storm, its duration,
and its depth. Also, analysis of the data from three sparsely located stations of coastal British
Columbia indicated that the time distribution of the storms does not change significantly over
the region.
With regard to the development of techniques for the better estimation of flood runoff,
a 24-hour design storm has been developed by using the data from the Seymour River
watershed. Analysis of its spatial distribution revealed that this 24-hour design storm is
distributed in a similar patter to that of the annual precipitation. Also, it was found that the
24-hour extreme raiiifall of various return periods is a certain percentage of the mean annual
precipitation. Comparison with regional data and results of other regional studies showed that
the developed design storm can be transposed over the whole coastal region of British
Columbia. A comparative study and rainfall-runoff simulation for a real watershed showed
that from the widely used synthetic hyetographs, only the Soil Conservation Service Type IA
storm or the 10% time probability distribution curve of this study can accurately generate the
flood runoff from watersheds of the region.
The above results of the short-term precipitation distribution with elevation and in time
were tested for extreme storms. Five periods of historical large flood producing storms were analyzed and it was shown that the fmdiiigs of the short-term precipitation analyses are valid
for these extreme storms.
The BOUNDP meteorological model was used for the estimation of storm
precipitation in the mountainous area which covers the two study watersheds, but the results
showed that this particular model is not capable of simulating the precipitation observed in the
area. As a result, the initial intention of coupling the model with a hydrological model for the
estimation of the runoff was abandoned.
The above results of the analysis of precipitation in coastal British Columbia and the
findings of previous research on the watershed response of coastal mountainous watersheds
have been combined and used for the development of a physically-based stochasticdeterministic
procedure. The procedure uses the method of derived distributions and Monte
Carlo simulation to estimate the flood frequency for ungauged watersheds of the region. The
procedure has been tested with data from eight coastal British Columbia watersheds and
compared with the results of other widely used regional techniques. This comparison showed
that the method is reliable and efficient, and requires very limited data, which can be found from a topographical map and the Rainfall Frequency Atlas for Canada.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/7036 |
| Date | 11 1900 |
| Creators | Loukas, Athanasios |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Relation | UBC Retrospective Theses Digitization Project [http://www.library.ubc.ca/archives/retro_theses/] |
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